The invention relates to a micropump as used especially for the delivery of small liquid drops from the air in laboratory apparatuses for chemical, in particular biochemical and medical investigations.
In the case of known micropumps of the generic type by means of which liquid drops are delivered from the air, the ejection orifice is usually located eccentrically in a larger, substantially flat, generally rectangular surface. Although EP 0 725 267 A2 proposed making the tip of a micropump pyramidal, no further information is given and it is to be assumed that it is actually intended to form a truncated pyramid in the relatively large flat front surface of which the ejection orifice is eccentrically located.
However, it has been found that a larger front surface surrounding the ejection orifice has a disadvantageous effect on the reliability of the ejection of the liquid drops and on the reproducibility of the drop size. This is due in particular to the fact that an accumulation of liquid concentrated around the ejection orifice readily forms on the front surface and influences the drop ejection in an uncontrollable manner and in certain circumstances even prevents said ejection.
It is the object of the invention to provide a micropump of the generic type in which the ejection of liquid drops takes place with high reliability and little variation of the drop size.
This object is achieved by the features in the claimed invention. The accumulation of liquid in the vicinity of the ejection orifice is as a rule avoided. However, even if such an accumulation of liquid nevertheless formsxe2x80x94for example because regulation of the liquid feed is not very precisexe2x80x94said accumulation remains slight and does not reach a troublesome amount since the liquid flows away laterally. The ejection of liquid drops thus takes place undisturbed and the drop size depends only on the properties of the liquid, on the size of the ejection orifice and on the control of the actuator.